Method for the manufacture of tantalum and/or niobium powder



United States Patent 3,415,639 METHOD FOR THE MANUFACTURE OF TAN- TALUM AND/0R NIOBIUM POWDER Gustav Daendliker, 'Birsfelden, Alex Jacob, Reinach,

Basel-Laud, and Walter Scheller, Muenclieustein, Switzerland, assignors to Ciba Limited, Basel, Switzerland, a company of Switzerland No Drawing. Filed'Apr. 5, 1966, Ser. No. 540,179 Claims priority, application Switzerland, May 25, 1965, 7,279/65 3 Claims. (Cl. 75-.5)

It is known to use sintered anodes of tantalum or niobium in the manufacture of electrolytic condensers. These anodes are manufactured from the corresponding metal powders. The electrical quality of the anode is affected by the chemical purity and particle size distr bution of the powder as well as by the surface in the sintered shape.

It has now been found that, especially for a high capacity yield, it is not only the 'abovementioned properties of the metal powder used for the anode manufacture which are important, but that additional properties which are determined by the method of manufacture of the metal powder are of great significance. It has been found that particularly advantageous metal powders for the manufacture of anodes may be obtained by thermite reduction. The present invention therefore relates to a method for the manufacture of tantalum and/or niobium powders which are suitable for the manufacture of sintered anodes for electrolytic condensers, characterised by reducing tantalum chloride and/or niobium chloride and/or tantalum oxide and/ or niobium oxide with magnesium metal and/ or calcium metal, optionally in the presence of alkali chlorides and/or alkaline earth chlorides, mixing the resulting metal powder, after washing out the salts in a manner which is in itself known, with, at most, the stoichiometric amount of carbon and/or carbide necessary for the formation of CO relative to the amount of oxygen present, purifying the mixture by sintering in vacuo at temperatures of 1600 to 2200 C., hydrogenating the sintered powder in a manner which is in itself known, grinding it and dehydrogenating it.

The reduction (or ignition) of the tantalum compounds and/or niobium compounds with magnesium metal and/ or calcium metal takes place in the manner which is usual for thermite reactions. The magnesium may be used in the form of filings, grit or powder, and an excess is advantageously employed. The reaction is preferably carried out in an inert gas atmosphere. The thermite composition may, if desired, also be diluted with alkali chloride and/or alkaline earth chlorides. The tantalum compounds and/or niobium compounds may be used in the form of oxychlorides or alternatively in the form of double chlorides with alkali chlorides. In a preferred embodiment of the present method, tantalum pentachloride is reduced with magnesium.

The purification of the metal powder obtained after washing, by treatment with carbon and sintering in vacuo, takes place in a manner which is in itself known. The carbon may be added in the form of carbon 'black or graphite or metal carbide. The use of graphite is preferred. Suitable sintering temperatures are those from 1600 to 2200 C. As a result of the sintering the metal powder is largely freed of metallic and non-metallic contaminants. Following the sintering the powder is hydrogenated in a manner which is in itself known, ground, and again dehydrogenated.

The subject of the present invention also comprises the use of the powders manufactured according to the invention for the manufacture of sintered anodes for electrolytic condensers, as well as the electrolytic condensers containing such sintered anodes. The manufacture of the 3,415,639 Patented Dec. 10, 1968 anodes and their incorporation into the electrolytic condensers takes place in a manner which is in itself known.

EXAMPLE 1 360 parts of powdered TaCl and 74 parts of magnesium grit are mixed under argon and poured into an Inconel tube. The Inconel tube is provided with an argon bypass and fixed in a vertical position. The tube wall is now heated to red heat at the level of the end of the charge, by means of a burner, as a result of which the reaction mixture is ignited'and burns in a downward direction. When the reaction has taken place the pipe wall is cooled with water and the product, which is a solidified salt melt pervaded with spongy metal, is taken out and broken up. The metal is isolated by several times leaching out the reaction mass with dilute hydrochloric acid followed by water, and subsequent filtration and drying in a vacuum cabinet. The material still contains the following impurities, in parts per million:

parts of this material, whose particle size at most reaches 250 are thoroughly mixed with 0.67 part of a fine graphite (particle size less than 40 1) and then pressed into porous tablets. The tablets are slowly heated to 1800 C. (pyrometrically determined, uncorrected) in a high vacuum furnace, and are then kept at this temperature for 30 minutes. The vacuum at the end of the heating period is 10" mm. Hg.

After cooling, the product is hydrogenated in the known manner. The hydrogenated tablets are broken up in a tantalum-lined stamping mill and are then sieved. This material is dehydrogenated in a high vacuum at 700 C. The free flowing powder exhibits the .following characteristics:

Specific surface (BET) Approx. 0.16 m. g. Oxygen content 1660 parts per million. Carbon content 25 parts per million. Nitrogen content 77 parts per million. Iron content 10 parts per million. Nickel content 10 parts per million. Chromium content .-e 10 parts per million. Magnesium content 1 part per million. Manganese content 1 part per million. Aluminum content 10 parts per million. Silicon content 10 parts per million.

For comparison purposes, a powder of similar purity and similar surface was produced from electrolytically deposited tantalum consisting of massive dendrites, by

hydrogenation and grinding.

Specific surface Approx. 0.17 mP/g. Oxygen content 1430 parts per million. Carbon content 58 parts per million. Iron content 10 parts per million. Nickel content 10 parts per million. Chromium content 10 parts per million. Magnesium content 1 part per million. Manganese content 1 part per million. Aluminum content 10 parts per million. Silicon content 10 parts per million.

Crude anodes are pressed from both powders.

The two types of anodes are now jointly sintered, with the final sintering temperature being about 2050 C. They are subsequently formed in 0.01% strength phosphoric acid at 200 volt, and their capacity is measured. A specific capacity of 2800;f-v. per g. of tantalum was found for the product manufactured according to the invention, and a specific capacity of 2380 .f-v. per g. of tantalum was found for the comparison powder.

EXAMPLE 2 Specific surface Approx. 0.15 mfl/ g. Oxygen content 2140 parts per million. Carbon content 108 parts per million. Nitrogen content 155 parts per million. Iron content 32 parts per million. Nickel content parts per million. Chromium content 10 parts per million.

What is claimed is: 1. A process for the manufacture of tantalum powders and niobium powders suitable for the manufacture of sintered anodes for electrolytic condensers, which oomprises reducing a member selected from the group consisting of tantalum chloride, tantalum oxychloride, niobium chloride, niobium oxychloride, tantalum oxide and niobium oxide with a member selected from the group consisting of magnesium metal and calcium metal, mixing the resulting metal powder, after washing out the salt in a manner which is in itself known, with at most the stoichiometric amount of a member selected from the group consisting of carbon and metal carbide required for the formation of CO relative to the oxygen content present, purifying by sintering in vacuo at temperatures of 1600 to 2200 C., hydrogenating the sintered powder in a manner which is in itself known, grinding it and dehydrogenating it.

2. A process according to claim 1 which comprises reducing TaCl with magnesium.

3. A process according to claim 1 which comprises using graphite.

References Cited UNITED STATES PATENTS 3,203,793 8/1965 Hand 174 3,295,951 1/1967 Fincham et a1. 750.5

FOREIGN PATENTS 657,781 2/1962 Canada.

L. DEWAYNE RUTLEDGE, Primary Examiner. 

1. A PROCESS FOR THE MANUFACTURE OF TANTALUM POWDERS AND NIOBIUM POWDERS SUITABLE FOR THE MANUFACTURE OF SINTERED ANODES FOR ELECTROLYTIC CONDENSERS, WHICH COMPRISES REDUCING A MEMBER SELECTED FROM THE GROUP CONSISTING OF TANTALUM CHLORIDE, TANTALUM OXYCHLORIDE, NIOBIUM CHLORIDE, NIOBIUM OXYCHLORIDE, TANTALUM OXIDE AND NIOBIUM OXIDE WITH A MEMBER SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM METAL AND CALCIUM METAL, MIXING THE RESULTING METAL POWDER, AFTER WASHING OUT THE SALT IN A MANNER WHICH IS IN ITSELF KNOWN, WITH AT MOST THE STOICHIOMETRIC AMOUNT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF CARBON AND METAL CARBIDE REQUIRED FOR THE FORMATION OF CO RELATIVE TO THE OXYGEN CONTENT PRESENT, PURIFYING BY SINTERING IN VACUO AT TEMPERATURES OF 1600 TO 2200*C., HYDROGENATING THE SINTERING POWDER IN A MANNER WHICH IS IN ITSELF KNOWN, GRINDING IT AND DEHYDROGENATING IT. 